DESCRIPTION

The LWP::UserAgent is a class implementing a simple World-Wide Web user agent in Perl. It brings together the HTTP::Request, HTTP::Response and the LWP::Protocol classes that form the rest of the core of libwww-perl library. For simple uses this class can be used directly to dispatch WWW requests, alternatively it can be subclassed for application-specific behaviour.

In normal usage the application creates a UserAgent object, and then configures it with values for timeouts proxies, name, etc. The next step is to create an instance of HTTP::Request for the request that needs to be performed. This request is then passed to the UserAgent request() method, which dispatches it using the relevant protocol, and returns a HTTP::Response object.

The basic approach of the library is to use HTTP style communication for all protocol schemes, i.e. you will receive an HTTP::Response object also for gopher or ftp requests. In order to achieve even more similarities with HTTP style communications, gopher menus and file directories will be converted to HTML documents.

The request() method can process the content of the response in one of three ways: in core, into a file, or into repeated calls of a subroutine. You choose which one by the kind of value passed as the second argument to request().

The in core variant simply returns the content in a scalar attribute called content() of the response object, and is suitable for small HTML replies that might need further parsing. This variant is used if the second argument is missing (or is undef).

The filename variant requires a scalar containing a filename as the second argument to request(), and is suitable for large WWW objects which need to be written directly to the file, without requiring large amounts of memory. In this case the response object returned from request() will have empty content(). If the request fails, then the content() might not be empty, and the file will be untouched.

The subroutine variant requires a reference to callback routine as the second argument to request() and it can also take an optional chuck size as third argument. This variant can be used to construct "pipe-lined" processing, where processing of received chuncks can begin before the complete data has arrived. The callback function is called with 3 arguments: the data received this time, a reference to the response object and a reference to the protocol object. The response object returned from request() will have empty content(). If the request fails, then the the callback routine will not have been called, and the response->content() might not be empty.

The request can be aborted by calling die() within the callback routine. The die message will be available as the "X-Died" special response header field.

The library also accepts that you put a subroutine reference as content in the request object. This subroutine should return the content (possibly in pieces) when called. It should return an empty string when there is no more content.

The user of this module can finetune timeouts and error handling by calling the use_alarm() and use_eval() methods.

By default the library uses alarm() to implement timeouts, dying if the timeout occurs. If this is not the prefered behaviour or it interferes with other parts of the application one can disable the use alarms. When alarms are disabled timeouts can still occur for example when reading data, but other cases like name lookups etc will not be timed out by the library itself.

The library catches errors (such as internal errors and timeouts) and present them as HTTP error responses. Alternatively one can switch off this behaviour, and let the application handle dies.

SEE ALSO

See LWP for a complete overview of libwww-perl5. See request and mirror for examples of usage.

METHODS

$ua = new LWP::UserAgent;

Constructor for the UserAgent. Returns a reference to a LWP::UserAgent object.

$ua->simple_request($request, [$arg [, $size]])

This method dispatches a single WWW request on behalf of a user, and returns the response received. The $request should be a reference to a HTTP::Request object with values defined for at least the method() and url() attributes.

If $arg is a scalar it is taken as a filename where the content of the response is stored.

If $arg is a reference to a subroutine, then this routine is called as chunks of the content is received. An optional $size argument is taken as a hint for an appropriate chunk size.

If $arg is omitted, then the content is stored in the response object itself.

$ua->request($request, $arg [, $size])

Process a request, including redirects and security. This method may actually send several different simple reqeusts.

The arguments are the same as for simple_request().

$ua->redirect_ok

This method is called by request() before it tries to do any redirects. It should return a true value if the redirect is allowed to be performed. Subclasses might want to override this.

The default implementation will return FALSE for POST request and TRUE for all others.

$ua->credentials($netloc, $realm, $uname, $pass)

Set the user name and password to be used for a realm. It is often more useful to specialize the get_basic_credentials() method instead.

$ua->get_basic_credentials($realm, $uri)

This is called by request() to retrieve credentials for a Realm protected by Basic Authentication or Digest Authentication.

Should return username and password in a list. Return undef to abort the authentication resolution atempts.

This implementation simply checks a set of pre-stored member variables. Subclasses can override this method to e.g. ask the user for a username/password. An example of this can be found in lwp-request program distributed with this library.

$ua->agent([$product_id])

Get/set the product token that is used to identify the user agent on the network. The agent value is sent as the "User-Agent" header in the requests. The default agent name is "libwww-perl/#.##", where "#.##" is substitued with the version numer of this library.

The user agent string should be one or more simple product identifiers with an optional version number separated by the "/" character. Examples are:

$ua->agent('Checkbot/0.4 ' . $ua->agent);
$ua->agent('Mozilla/5.0');

$ua->from([$email_address])

Get/set the Internet e-mail address for the human user who controls the requesting user agent. The address should be machine-usable, as defined in RFC 822. The from value is send as the "From" header in the requests. There is no default. Example:

$ua->from('aas@sn.no');

$ua->timeout([$secs])

$ua->use_alarm([$boolean])

Get/set a value indicating wether to use alarm() when implementing timeouts. The default is TRUE, i.e. to use alarm. Disable this on systems that does not implement alarm, or if this interfers with other uses of alarm in your application.

$ua->use_eval([$boolean])

Get/set a value indicating wether to handle internal errors internally by trapping with eval. The default is TRUE, i.e. the $ua->request() will never die.

$ua->parse_head([$boolean])

Get/set a value indicating wether we should initialize response headers from the <head> section of HTML documents. The default is TRUE. Do not turn this off, unless you know what you are doing.

$ua->clone;

Returns a copy of the LWP::UserAgent object

$ua->is_protocol_supported($scheme)

You can use this method to query if the library currently support the specified scheme. The scheme might be a string (like 'http' or 'ftp') or it might be an URI::URL object reference.

$ua->mirror($url, $file)

Get and store a document identified by a URL, using If-Modified-Since, and checking of the Content-Length. Returns a reference to the response object.